Crank chamber compression-type two-cycle engine

ABSTRACT

A crank chamber compression-type two-cycle engine wherein an intake passage is communicated with the interior of a cylinder through an intake port which is opened and closed by a piston disposed in the cylinder for reciprocal motion therein, and a crank chamber and the combustion chamber in the cylinder are communicated with each other through a scavenging port, opened and closed by the piston, and a scavenging passage.

UEBiEQ States atent Nomura 1 Aug. 29, 1972 [54] CRANKCHAMBERCOMPRESSION- 3,530,841 9/ 1970 Schultz ..123/73 R TYPE TWO-CYCLE ENGINE890,335 6/1908 Claus ..'....'...123/'73 PP 3,107,659 10/1963 Steinleinet al. ..123/73 V [72] Invenmr' f Nmnum Hamamatsu 1,149,296 8/1915 Scottet a1. ..123 73 B 1,239,488 9/1917 Hoshe1.. ..l23/73 V 1 1 AsslgneerYamaha Hatsudakl, Kapushlkl 980,134 12/1910 Springer ..123/73 v Kaisha,Hamukita-sh1, Sh1zuokaken, Japan FOREIGN PATENTS OR APPLICATIONS [22]Filed: July 10, 1970 615,162 12/1926 France ..123/73 B [21] Appl No:53,949 504,909 8/1930 Germany ..123/73 C Primary Examiner-Wendell E.Burns [30] Foreign Application Priori y a Assistant Examiner-A. M.Zupcic July 14, 1969 Japan ..44/55652 Attorney-JO Lezdey Aug. 26, 1969Japan ..44/81051 ABSCT [52] US. Cl ..l23/73 R, 123/73 A, 123/73 B, Acrank chamber compressiomtype two cyc1e engine 123/73 123/73 PP whereinan intake passage is communicated with the [51] 111i. Cl ..F02b 33/04interior of a cylinder through an intake port which is [58] new ofSearch "123/73 73 73 73 opened and closed by a piston disposed in thecylinder 123/73 B, 65 A, 65 E, 73 C, 65 WV for reciprocal motiontherein, and a crank chamber 56 R f CM and the combustion chamber in thecylinder are com- 1 e erences l municated with each other through ascavenging port, UNITED STATES PATENTS opened and closed by the piston,and a scavenging assa e. 1,346,001 7/1920 Casey ..123 73 v p g 996,4346/1911 Talley ..123/73 A 7 Claims, 6 Drawing Figures P'ATENTEDwm I9123,687.1 l8

SHEEI 2 0F 3 INVENTOR KAZUHIKO NOMURA ATTORNE 3Q687ll18 PAIENTEDauszsI972 SHEET 3 OF 3 INVENTOR KAZUHIKO NOMURA BY ATTORN CRANK CHAMBERCOMPRESSION-TYPE TWO- CYCLE ENGINE BACKGROUND OF THE INVENTION Thisinvention relates to a two-cycle internal combustion engine andparticularly to a crank chamber compression-type two-cycle engine. Moreparticularly, the invention relates to a crank chamber compressiontypetwo cycle engine of the type wherein an intake passage is communicatedwith a crank chamber through an intake port which is opened and closedby a piston reciprocating in a cylinder, and the crank chamber iscommunicated with the combustion chamber in the cylinder through ascavenging port, opened and closed by said piston, and a scavengingpassage.

DESCRIPTION OF THE PRIOR ART In a crank chamber compression-typetwo-cycle engine, it is well known to provide in the intake passagecommunicating directly with the crank chamber a reed valve which passesa gas flowing in a direction toward the crank chamber but blocks a gasflowing in an opposite direction. In the ordinary crank chambercompression-type two-cycle engines having an intake port which is openedand closed by a piston reciprocating in a cylinder, the timing at whichthe piston begins to open the intake port is about 80 or less than 100at most, before the top dead center, whereas in the enginesincorporating the aforesaid reed valve the timing at which the reedvalve begins to be opened is about 160 200 before the top dead center asresult. It is also known that the two-cycle engines of the typeincorporating such reed valve have the advantage that an improved powercan be obtained during normal operation, because they have longer intakeperiod.

On the other hand, the two-cycle engines having the reed valve providedin the intake pipe have the disadvantage that starting of the engine isdifficult due to the fact that the intake air flow at the engine startspeed is relatively low.

SUMMARY OF THE INVENTION The primary object of the present invention isto eliminate the above-described disadvantage of the crank chambercompression-type two-cycle engine having a reed valve provided in theintake passage.

According to one aspect of the present invention, there is provided acrank chamber compression-type two-cycle engine wherein an intakepassage is communicated with a crank chamber through an intake portwhich is opened and closed by a piston reciprocating in a cylinder, andthe crank chamber is communicated with the combustion chamber in thecylinder through a scavenging port, opened and closed by said piston,and a scavenging passage, characterized in that said intake passage isprovided therein with a reed valve which passes a gas flowing in adirection toward the crank chamber but blocks a gas flowing in anopposite direction, and the opening timing of said intake port isselected within the range from 140 to 100 before the top dead center.

According to the feature of the invention set forth above, the powerincreasing effect of the reed valve, provided in the intake passage, canbe sufi'iciently achieved and the intake air flow speed at the enginestart becomes sufficiently high, so that starting of the engine becomesrelatively easy. It is known that when the intake port opening timing isadvanced from about 140 before the top dead center, a sufficiently highintake air flow speed cannot be obtained at the engine start and hencestarting of the engine becomes difficult, whereas when the same isretarded from before the top dead center, the power increasing effect ofthe reed valve cannot be obtained.

According to another aspect of the invention, there is provided atwo-cycle engine of the character described above, wherein the intakepassage is communicated with the interior of the cylinder through anauxiliary scavenging passage and an auxiliary scavenging port, at apoint downstream of the reed valve and said auxiliary scavenging port isopened and closed with substantially the same timing as the mainscavenging port. With such arrangement of the invention, the scavengingefficiency in the interior of the cylinder can be drastically enhancedand the burned gas residing in the cylinder can be completely scavenged.

According to still another aspect of the invention, there is provided atwo-cycle engine of the character described above, wherein a fuelinjection nozzle is provided in the auxiliary scavenging passage and areed valve which opens only in a direction toward the cylinder isprovided at the point where the auxiliary scavenging passage opens inthe intake passage. In this case, the auxiliary scavenging port openingtime is slightly retarded from the main scavenging port opening time,whereby the cylinder is at first scavenged with air only and then afuel-air mixture is introduced into the cylinder. Therefore, the rate offuel consumption can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of anembodiment of the two-cycle engine according to the present invention;

FIG. 2 is a diagram graphically showing the intake air flow speed;

FIG. 3 is a cross-sectional view of another embodiment of the two-cycleengine according to the invention;

FIG. 4 is a transverse cross-sectional view taken along the line AA ofFIG. 3;

FIG. 5 is a cross-sectional view of a modification of the engine shownin FIG. 3; and

FIG. 6 is a cross-sectional view of still another embodiment of theengine of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. I, theengine generally indicated by numeral 1 has a cylinder 2 and a piston 3disposed in said cylinder for reciprocal motion therein, and a crankchamber 8 is formed beneath the cylinder 2 which is enclosed by a crankcase 11. An intake pipe 6 having a carburetor 5 is communicated with thecrank chamber 8 through an intake port 4 which is opened and closed bythe vertically reciprocating piston 3. The intake pipe 6 is alsoprovided therein with a reed valve 7 between the intake port 4 andcarburetor 5. This reed valve 7 is operative in such a manner that itpasses a gas flowing in a direction toward the crank chamber 8 butblocks a gas flowing in an opposite direction. The cylinder 2 isprovided with an exhaust port 9. The piston 3 is connected to a crankshaft 13 by a connecting rod 10. Numeral l2 designates a scavengingpassage provided in a conventional manner. In the present invention, thetiming at which the piston 3 begins to open the intake port 4 isselected within the range from 100 to 140 before the top dead center,and is 100 before the top dead center in the embodiment shown.

.The function of the intake device of the invention will be describedwith reference to FIG. 2. A curve a of FIG. 2 shows the relationshipbetween the crank angle and the intake air flow speed of a conventionalengine having a reed valve in the intake passage, and a curve b showsthe same of the engine according to the invention now underconsideration. As will be clear from the diagram, in the conventionalengine the suction starts at a point about 160 before the top deadcenter, and the intake air flow speed increases gradually and thendecreases gradually. In the present invention, as contrasted thereto,the intake air flow speed sharply increases at a point slightly beyondthe point 100 before the top dead center and the fuel-air mixture isagitated vigorously. The intake air quantities in both engines,

which are represented by the areas defined by thecurves and b aresubstantially the same.

Thus, it will be understood that according to the instant invention, ascompared with the case wherein use is made only of a reed valve, anequally high power can be obtained and in addition, the startingcharacteristic of the engine can drastically be improved since the intake air flow speed is higher.

FIG. 3 shows another embodiment of the invention in which thecorresponding parts are indicated by the same numerals as in FIG. 1. Inthis embodiment, a reed valve 7 which permits the fuel-air mixture toflow from a carburetor 5 to an intake port 4 but blocks the same flowingin an opposite direction, comprises a valve seat 7a of a V-shape incross-section having openings '75, reed members 7c connected to saidvalve seat 7a so as to open and close said respective openings 7 b andstoppers 7d to restrain the movement of said reed members 70. Further,in this embodiment an auxiliary scavenging passage is provided which isopen at one end into the intake passage 6 at a point between the reedvalve, and at the other end 7 and the intake port 4 or downstream of thereed valve, and at the other end into a cylinder 2 through an auxiliaryscavenging port 14. The auxiliary scavenging port 14 is locatedsubstantially immediately above the intake port 4, and it is most idealthat the auxiliary scavenging port begins to be opened slightly beforethe intake port 4 is completely closed but such timing is alwaysnecessary because the intake air has an inertia and there is an pressureaccumulating effect in the intake passage.

In this embodiment, when the intake port 4 is opened by the side wall ofthe piston 3, the fuel-air mixture from the carburetor 5 flows into thecrank chamber 8 through the intake port 4 after forcibly opening thereed members 7c of the valve 7 and passing through the intake passage 6.The fuel-air mixture in the crank chamber 8 is preliminarily compressedby the bottom of the piston 3 and then injected into the cylinder fromthe crank chamber g through a main scavenging passage 12 when the mainscavenging port is opened by the side wall of the piston 3. On the otherhand, the auxiliary scavenging port M is concurrently opened, so thatthe fuel-air mixture in the crank chamber 8 is led into the intakepassage 6 through the intake port 4 and injected into the cylinder 2 viathe auxiliary scavenging passage 15. In this case, the fuel-air mixtureentering the intake passage 6 is not permitted to flow back into thecarburetor since the openings 72; of the valve 7 are closed by the reedmembers 70.

The fuel-air mixture thus injected into the cylinder 2 through the mainscavenging port and the auxiliary scavenging port 14 scavenges theburned gas in said cylinder into an exhaust passage 9 and the interiorof the cylinder has almost entirely been filled with the fresh gas.Another embodiment shown in FIG. 5 is a modification of the engine ofFIGS. 3 and 4, in which an elongate recess is formed in the side wall ofthe cylinder 2 to define an auxiliary scavenging passage 15' by the sidewall of the piston 3 and the wall of said elongate recess, so as tofacilitate the provision of the auxiliary scavenging passage and theproduction of the engine only by a modification of the presentlyavailable engines. The other construction is the same as that of theengine shown in FIGS. 3 and 4.

The construction of the engine shown in FIG. 6 is essentially similar tothat of the engine of FIGS 3 and 4, but in this embodiment thecarburetor is not provided in the intake passage 6 and a fuel injectionnozzle 16 is provided in the auxiliary scavenging passage 15 and furthera reed valve 117 which is open only toward the cylinder 2 is provided atthe point where the auxiliary scavenging passage 15 opens into theintake passage 6. According to this arrangement, any adverse effects onthe operation of the reed valve 7 can be eliminated because the pressurefluctuation within the cylinder does not have direct influence on thepressure in the intake pipe 6 and, moreover, the rate of fuelconsumption can drastically be enhanced by slightly retarding theopening time of the auxiliary scavenging port from the opening time ofthe main scavenging port.

I claim:

1. A crank chamber compression-type two-cycle engine comprising acylinder, a piston disposed in said cylinder for reciprocal motiontherein, a crank chamber, a crank shaft rotatably supported in saidcrank chamber, a connecting rod connecting said piston to said crankshaft, a scavenging passage means communicating said crank chamber withsaid cylinder through at least one scavenging port which is open in theside wall of the cylinder and opened and closed by the piston, an intakepassage means communicating with said crank chamber through an intakeport which is opened and closed by said piston, said intake passagemeans being connected to said cylinder at a point downstream of saidcheck valve means through an auxiliary scavenging passage means which isopen into the cylinder through an auxiliary scavenging port opened andclosed by the piston, an exhaust passage means communicating with theinterior of said cylinder and a check valve means provided in mid intakepassage means and being operative in such a manner that it passes a gasflowing in a direction toward said crank chamber but blocks a gasflowing in an opposite direction, the opening timing of said intake portbeing located 140 to 100 before the top dead center whereby the intakeair flows into the cylinder continuously.

2. A crank chamber compression-type two-cycle engine as defined in claim1, wherein a carburetor is provided in said intake passage means and afuel-air mixture is introduced into said crank chamber.

3. A crank chamber compression-type two-cycle engine as defined in claim1, wherein said check valve means is a reed valve comprising a V-shapevalve seat having at least one opening and at least one reed memberconnected to said valve seat for closing said opening and adapted to beopened with pressure exerted thereon in one direction through theopening in the valve seat.

4. A crank chamber compression-type two-cycle engine as defined in claim1, wherein said auxiliary scavenging passage means is provided thereinwith a check valve being operative in such a manner that it passes a gasflowing in a direction toward the cylinder but blocks a gas flowing inan opposite direction.

5. A crank chamber compression-type two-cycle engine as defined in claim1, wherein said auxiliary scavenging passage means is provided thereinwith a fuel injection nozzle and a check valve positioned on the intakepassage side with respect to said nozzle and being operative in such amanner that it passes a gas flowing in a direction toward the cylinderbut blocks a gas flowing in an opposite direction.

6. A crank chamber compression-type two-cycle engine as defined in claim1, wherein said auxiliary scavenging passage means consists of a grooveformed in the wall of the cylinder.

7. A crank chamber compression-type two-cycle engine as defined in claim5, wherein said auxiliary scavenging port is opened with a slight delayafter the main scavenging port is opened.

8. A crank chamber compression-type two cycle engine comprising acylinder, a piston disposed in said cylinder for reciprocal motiontherein, a crank chamber, a crank shaft rotatably supported in saidcrank chamber, a connecting rod connecting said piston to said crankshaft, a scavenging passage means communicating said crank chamber withthe interior of said cylinder through at least one scavenging port whichis open in the side wall of the cylinder and opened and closed by thepiston, an intake passage means communicating with said crank chamberthrough an intake port which is opened and closed by said piston, anexhaust passage means communicating with the interior of said cylinder,a check valve means provided in said intake passage means and beingoperative in such a manner that it passes a gas flowing in a directiontoward said crank chamber but blocks a gas flowing in an oppositedirection, and an auxiliary scavenging passage means communicating saidintake passage means with said cylinder at a point downstream of saidcheck valve means through a port which is opened and closed by thepiston.

1. A crank chamber compression-type two-cycle engine comprising acylinder, a piston disposed in said cylinder for reciprocal motiontherein, a crank chamber, a crank shaft rotatably supported in saidcrank chamber, a connecting rod connecting said piston to said crankshaft, a scavenging passage means communicating said crank chamber withsaid cylinder through at least one scavenging port which is open in theside wall of the cylinder and opened and closed by the piston, an intakepassage means communicating with said crank chamber through an intakeport which is opened and closed by said piston, said intake passagemeans being connected to said cylinder at a point downstream of saidcheck valve means through an auxiliary scavenging passage means which isopen into the cylinder through an auxiliary scavenging port opened andclosed by the piston, an exhaust passage means communicating with theinterior of said cylinder and a check valve means provided in saidintake passage means and being operative in such a manner that it passesa gas flowing in a direction toward said crank chamber but blocks a gasflowing in an opposite direction, the opening timing of said intake portbeing located 140* to 100* before the top dead center whereby the intakeair flows into the cylinder continuously.
 2. A crank chambercompression-type two-cycle engine as defined in claim 1, wherein acarburetor is provided in said intake passage means and a fuel-airmixture is introduced into said crank chamber.
 3. A crank chambercompression-type two-cycle engine as defined in claim 1, wherein saidcheck valve means is a reed valve comprising a V-shape valve seat havingat least one opening and at least one reed member connected to saidvalve seat for closing said opening and adapted to be opened withpressure exerted thereon in one direction through the opening in thevalve seat.
 4. A crank chamber compression-type two-cycle engine asdefined in claim 1, wherein said auxiliary scavenging passage means isprovided therein with a check valve being operative in such a mannerthat it passes a gas flowing in a direction toward the cylinder butblocks a gas flowing in an opposite direction.
 5. A crank chambercompression-type two-cycle engine as defined in claim 1, wherein saidauxiliary scavenging passage means is provided therein with a fuelinjection nozzle and a check valve positioned on the intake passage sidewith respect to said nozzle and being operative in such a manner that itpasses a gas flowing in a direction toward the cylinder but blocks a gasflowing in an opposite direction.
 6. A crank chamber compression-typetwo-cycle engine as defined in claim 1, wherein said auxiliaryscavenging passage means consists of a groove formed in the wall of thecylinder.
 7. A crank chamber compression-type two-cycle engine asdefined in claim 5, wherein said auxiliary scavenging port is openedwith a slight delay after the main scavenging port is opened.
 8. A crankchamber compression-type two cycle engine comprising a cylinder, apiston disposed in said cylinder for reciprocal motion therein, a crankchamber, a crank shaft rotatably supported in said crank chamber, aconnecting rod connecting said piston to said crank shaft, a scavengingpassage means communicating said crank chamber with the interior of saidcylinder through at least one scavenging port which is open in the sidewall of the cylinder and opened and closed by the piston, an intakepassage means communicating with said crank chamber through an intakeport which is opened and closed by said piston, an exhaust passage meanscommunicating with the interior of said cylinder, a check valve meansprovided in said intake passage means and being operative in such amanner that it passes a gas flowing in a direction toward said crankchamber but blocks a gas flowing in an opposite direction, and anauxiliary scavenging passage means communicating said intake passagemeans with said cylinder at a point downstream of said check valve meansthrough a port which is opened and closed by the piston.